1. Field of the Invention
The present invention relates to antifuses and to structures and methods for programming antifuses. More particularly, the present invention relates to programming of antifuses using silicon controlled rectifier (SCR) and bipolar transistor structures.
2. The Prior Art
Amorphous silicon is commonly employed as the antifuse material in antifuses. Antifuses employing amorphous silicon antifuse layers require high programming currents (on the order of 15 to 30 mA or more) to prevent the programmed antifuse from later switching back to its off state. Prior art integrated circuits employing amorphous silicon antifuses employ large-area MOS transistors on the integrated circuit die in order to supply the high programming currents necessary for use in programming such antifuses. In these prior art integrated circuits, a first MOS transistor is a pull-up transistor having a source/drain region connected to a first electrode of the antifuse so that a programming voltage can be placed on that electrode, and a second MOS transistor is a pull-down transistor having a source/drain region connected to a second electrode of the antifuse so that an intermediate or ground voltage can be placed on that electrode.
In integrated circuits such as field programmable gate array integrated circuits containing large numbers (thousands to hundreds of thousands) of antifuses, the die area cost of providing the number of necessary MOS programming transistors is significant. As such arrays increase in size and density, the additional area required to provide programming transistors also increases. Die size limitations due to defect density will serve to limit the size of arrays which can be economically manufactured.
It would therefore be advantageous to provide small-area switching devices for use in amorphous silicon antifuse arrays which are capable of supplying the current necessary to program amorphous silicon antifuses. An object of the present invention is to therefore provide small-area switching devices for use in amorphous silicon antifuse arrays which are capable of supplying the current necessary to program amorphous silicon antifuses.